THE RED-SHANKED DOUC
OF SON TRA

In the province of Quang Nam in central Vietnam, lies Danang, the country’s fifth most populous city known for its beaches, peninsulas, history and natural wonders.

This city of over a million inhabitants lies at the edge of a belt of Palaeozoic folds known as the Truong Son orogenic zone, whose main deformation occurred in the early Carboniferous period. To the west, the area is dominated by the majestic foothills of the Annamite chain. To the east lie white sandy beaches and the Son Tra peninsula, crossed by the Song Qua Giang River.

Danang’s origins date back to the ancient Cham kingdom of Indrapura, and its remains can be found in the ancient Cham city of Singhapura (the “Lion City”). Its location corresponds to the village of Tra Kieu, not far from the My Son valley, another remarkable Champa site. Under pressure from the Dai Viet, the Cham abandoned Indrapura around 1000 AD. French ships sent by Admiral Cécille bombarded Danang in 1847, and in August 1858, French troops led by Admiral Charles Rigault de Genouilly (under the orders of Napoleon III) landed in Danang Bay. The French renamed the city Tourane and placed it under the control of the Governor-General of French Indochina. During the Vietnam War, Danang was a major base for South Vietnamese and American forces. On 30 March 1975, the town was taken by North Vietnamese forces.

To the south of this now booming city, majestic white sandy beaches stretch as far as Hoi An (Faifo or Phai Pho) and the Song Thu Bon estuary. Around ten km to the north, the Song Tra nature reserve rises like a hammer. Dominated by three peaks (the highest is Mount Son Tra at 693m), the “monkey mountain” – as it was called by the Americans during the Second Indochina War – is 13 km long and six km wide, covering an area of 4,439 hectares. It is covered by 4,180 hectares of tropical maritime forest that creates a sort of natural screen against storms. This green lung, which regulates the local climate, is home to 287 species of flora and fauna. Twenty-nine of them are considered rare, including the red-shanked douc (Pygathrix nemaeus), a species of primate in the Cercopithecidae family, also known as the five-colored monkey, the costumed monkey, the Son Tra langur, or the Queen of the Primates. The taxon also includes the black-shanked douc (P. nigripes) and the grey-shanked douc (P. cinerea).

Today, the largest wild population of this native southeast Asian species is found in eastern Laos, in the almost contiguous national parks of the Nakai-Nam Theun National Biodiversity Conservation Area (NBCA), which has an estimated population of 4,500, and Hin Namno NBCA. The red-shanked douc can also be seen in the Xe Xap NBCA, and it is likely that it also lives in other remote areas of the country where data is lacking. In Cambodia, a few individual doucs were observed in 2007 in Ratanakiri Province, while in Vietnam, the population (apparently overestimated) is believed to number around 2,000 in both Phong Nha-Ke Bang National Park and Son Tra – an increase since the last enumeration in 2017, which counted 1,300 red-shanked doucs. Further south, Chu Mom Ray National Park may also be home to a few specimens, representing a possible area of sympatry and/or hybridisation, but the taxonomic status of the species there is uncertain.

Like the other doucs, Pygathrix nemaeus is a long, slender monkey, measuring around 60 cm with a tail that ranges from 56 to 76 cm. Its colorful coat is grey on its back and belly; black on its thighs, hands and feet; reddish-brown on its legs; and white on its tail and forearms. Its face is ochre with a white nose, with light blue eyelids, a black forehead, and white cheeks and throats. Males weigh between eight and 11 kg, while females weigh between six and ten kg.

This striking, shy primate thrives in primary and secondary evergreen and semi-evergreen forests, deciduous forests, mixed deciduous and coniferous forests, and karst forests at altitudes ranging from sea level to around 1,700 m (and probably higher). Diurnal and arboreal, it sometimes comes to the ground. Its diet consists mainly of leaves (it is particularly fond of young shoots and buds), followed by fruit, seeds, flowers, bark and marrow. It does not drink; the water it ingests comes solely from its food, thanks to its complex digestive system, which enables it to extract essential nutrients.

Pygathrix nemaeus often lives in mixed groups of four to 18, and sometimes up to 50, mixed individuals. It lives in a modular society characterised by the fission-fusion of several single-person units that assemble and divide on a daily basis. To communicate, they use a range of facial expressions, combining a low growl as a threat with a short, harsh distress call. Males and females have their own hierarchies, with males dominating females. These individuals generally do not remain in their birth group.

Now critically endangered, Pygathrix nemaeus is thought to have suffered a decline of more than 80% over the last three generations (36 years), due to encroachment and forest loss across its range caused by dams, road infrastructure development, agricultural plantations, mining, and intensive hunting for the lucrative wildlife trade. Thanks to the efforts of GreenViet Biodiversity Conservation Centre (a local non-profit organisation established in 2012) and other conservationists, the population of Pygathrix nemaeus in Son Tra Nature Reserve has been growing again in recent years.

These specimens can be observed in the jungle from the prestigious InterContinental Danang Sun Peninsula Resort. This oasis, designed by the renowned architect Bill Bensley, blends into its setting of tropical palm trees, with its feet in the water. It comprises 189 rooms, suites, penthouses and villas, all elegantly decorated in a Vietnamese vernacular style that follows a thematic palette of hues fluctuating from the black of lacquered wood to the white of the tiles of the emblematic temples, mixed with judiciously placed colors and unique works of art, with a breathtaking view of the azure eastern sea. All in all, the InterContinental Danang Sun Peninsula is a world-class resort with unrivalled service and design that sets a benchmark in the world of prestige hotels.

CAPTIONS

- Banner: the red-shanked douc, by Eric Losh.
- Photo: two Pygathrix nemaeus of the Cuc Phuong Endangered Primate Rescue Center, by Joel Sartore.
- Illustration: the red-shanked douc, Collection Abecasis Science.

 

---

During various Ke Bang missions in 2024, one of the wonders we observed was the hsienmu. In this winter edition, we take a look at this exquisite species from the limestone heights of Southeast Asia.

The hsienmu is a rare, majestic tree scattered in the form of localized woods. It thrives on the karst massifs of central and northern Vietnam, northeastern Laos, and southern China. It is characterized by its cracked bark, powerful tentacular roots, and construction qualities.

For nearly 30 years, the hsienmu has been threatened by habitat loss. Since 1998, it has been included in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species and classified as vulnerable according to A1cd criteria. In Vietnam, various conservation actions are underway, notably in the Ba Be and Phong Nha-Ke Bang National Parks.

The hsienmu (Burretiodendron hsienmu, the Nghien of the Vietnamese) is classified in the Dombeyoideae subfamily of the Malvaceae family. It thrives in tropical and subtropical rainforests at altitudes ranging from 500 to 1,500m, growing on well-drained karst soil. It requires a warm, humid climate to thrive and has adapted to environments with moderate to high temperatures and high humidity, such as the misty summits of Phu Tha Ca as well as the Ba Be and Phong Nga-Ke Bang National Parks.

The hsienmu can reach heights of 30 to 50m, with an average diameter of 80 to 90 cm, sometimes more for older specimens (around 3.5m). Some venerable specimens can reach an age of 1,000 and 2,000 years, notably in the forest of Ha Lang district, Cao Bang Province (northeast Vietnam) and the Gulinqing Nature Reserve (south Yunnan).

Its trunk is straight and sturdy, with grey to brownish bark that is sometimes cracked. Young branches are hairless. Leaves are oval, about 12 cm long and 10 cm wide, with a full margin. They have between five and seven pairs of lateral veins – three of which start from the base – with a leaf petiole that ranges from three to five centimeters long.

Flowers are unisexual. Male flowers are about 1.5 cm in diameter, with a bell-shaped calyx divided into five deep lobes approximately 1.5 cm long. There are five petals, each typically 1.3 cm long. They have around 25 stamens grouped in five clusters; stamen threads are between 1 and 1.3 cm long, and oblong anthers three millimeters long. The fruit is pentagonal (similar to a peach tree fruit), naturally opening with a diameter of 1.8 cm, and it ripens in late summer or autumn.

The hsienmu produces fruits and seeds that serve as food for a variety of forest creatures. Birds, small mammals, and even some insects feed on the seeds, helping to disperse them. The nutrient-rich fruits attract many herbivores and omnivores, establishing the tree as an essential food source. The hsienmu bark, leaves, and wood harbor multitudes of insects. These insects, in turn, attract predators such as insectivorous birds and small reptiles. By providing a habitat and food source for these insects, the tree indirectly supports higher trophic levels.

Once they have fallen to the ground, dead leaves, branches, and other vegetative parts of the hsienmu are decomposed by a variety of decomposer organisms, such as fungi, bacteria, and saprophagous insects. These decomposers transform organic matter into plant-available nutrients, thus closing the nutrient cycle in the forest. The tree’s deep, extensive roots help stabilize the soil and prevent erosion. By binding the soil, the tree helps maintain the structure of the forest floor, protecting against landslides and erosion caused by heavy monsoon rains.

As a large tree, the hsienmu plays a crucial role in regulating the forest microclimate of the limestone mountains of central and northern Vietnam. Its dense foliage provides shade, moderating ground temperatures and reducing evaporation. It absorbs carbon dioxide from the atmosphere and stores it in the form of biomass. This carbon sequestration function helps mitigate the effects of climate change by reducing the concentration of greenhouse gases in the atmosphere.

Hsienmu wood has high mechanical properties. It is very hard, resistant, durable, grain-free and impervious to insects and fungi, even when buried in the ground. Weathering can only dull the exposed wood surface. Its heartwood is uniformly dark brown, with very fine growth rings and a layered structure. When polished, older parts can reveal subtle patterns similar to those on the blade of a Japanese sword – a rare phenomenon due to the wood’s layered structure, also known as chun grain, which only a few types of wood possess.

The inhabitants of the high limestone mountain regions of Vietnam, mainly the Tâys, Hmôngs and Nungs, use hsienmu to build their houses, including posts, floors, crossbeams, main beams, and other elements. A distinctive feature of this wood is that, when walked on, it never produces the characteristic sound of soft or flexible wood, which is why it is highly prized for making planks. It is also used for partitions, shelves, tables, and chairs. The knots in its trunk (the gnarled parts or woody growths that form when the tree trunk is injured or has an abnormality) have a rough surface but are made of hardwood, with a variety of colors and aesthetic knot patterns. They are used to make decorative crafts such as sculptures, vases, and decorations.

On request, Secret Indochina can organize modules to observe the hsienmu in its natural environment. These are mainly in the Ba Be and Phong Nha-Ke Bang National Parks and at the Phu Tha Ca, from the white hmông village of Seo Lung where forest walks wend through the central valley of this misty massif, the second highest point in Ha Giang Province.

CAPTIONS

- Banner: hsienmu leaf.
- Photo #1: centenarian hsienmu (Cao Bang).
- Photo #2: millennial hsienmu (Gulinqing Natural Reserve, China).